The invention described herein was made in part in the course of work under a grant or award from the National Science Foundation.
1. Field of the Invention
This invention relates generally to the field of Mining or in Situ Disintegration of Hard Material, and more particularly to Expansible Breaking Down Devices having fluid pressed pistons and wedges.
2. Description of the Prior Art
Pressure breakers or rock-splitters are well known in the art and are exemplified by the patents to Darda:
U.s. pat. No. 3,414,328 Hydraulically Actuated Tool for the Mechanical Breaking of Rocks by Means of a Wedge Slidable through Insert Pieces PA1 U.s. pat. No. 3,488,093 Pressure Breaker PA1 U.s. pat. No. 3,791,698 Hydraulically Operated Apparatus for Mechanical Splitting of Rock and the Like
Each of the above patents shows a rock-splitter of the general type involved in the present invention. The splitters each have two or more elongate, wedge-like pressure bars or feathers adapted to be inserted into a pre-drilled hole in a rock or other hard substance, and an elongate central sliding wedge or spreader adapted to be driven axially between the feathers. The driving force for the spreader is most commonly provided by a hydraulic piston which is actuated by high fluid pressure. The total force acting axially on the spreader is the product of the fluid pressure times the area of the piston, and this force is transformed into a radial force and is multiplied manyfold by the mechanical advantage of the feather-spreader configuration. The feathers at first move radially to the diameter of the pre-dilled hole and the radial force generated by the pressure bars then builds up until it is of sufficient magnitude to cause the rock to fracture.
Impact hammers or drills are also well known in the art. Such drills most commonly comprise in elongate cylinder and a heavy metal piston disposed to move longitudinally within the cylinder. Air or other fluid under pressure is supplied from a suitable compressor source and is admitted by suitable valves into the cylinder to cause the piston to oscillate therein. The momentum of the piston is imparted as an impact force against an anvil disposed in the working end of the cylinder. The anvil in turn drives a drill or wedge against a rock or paving to fracture the same. The impact force imparted to the rock may have a peak value in excess of 50,000 lbs.
A U.S. Pat. to Amtsberg, No. No. 3,796,271 teaches a triple coaxial hammer comprised of three hammer elements in telescopic relation for driving a rock drill. Amtsberg's hammer is hydraulically movable on a work stroke, and is returnable by hydraulic force supplemented by force of pressure air. This arrangement provides a relatively wide impact pulse against the drill. It is not used in conjunction with a rock splitter and does not combine the hydraulic and pneumatic forces for driving the drill.